Hello Siggi,
Thank you for your suggestions,
I'll try checking the leakage in the store capacitors (10MOhm probe is ok for that IMHO).
A1 board was repaired ("butchered" by me) from above without unscreweing and removing is at all. I.e. the opamps desoldering in the CHANNEL 1 and the hybrid replacement was done by keeping the A1 board in place (my fault).
It seems like I would have to do more substantial time investment, remove A1 and recap the board and finally verify/replace C851-C854 caps.
Also I follow Chuck's recommendation about the raster adjustment since I've never done that before.
On top of that I've measured the old removed electrolytic caps from A5 and they seem to be fine. Low ESR, good capacitance, very low self-discharge current. But in the power supply the most of the caps were really bad. Also A1 runs in much tougher temperature mode, so likely the recapping is necessary also.
looking at the schematics just noticed, that the -1.25V and +1.36 references from A5 are used on A1 all over the place.
